PROJECT SUMMARY Isoforms of ApoE modify the risk for developing Alzheimer?s disease (AD) or cardiovascular disease, and are also associated with exceptional longevity. Specifically, the e2/e2 genotype is associated with exceptional longevity while the e4 allele is negatively associated with longevity. The e4 variant of the ApoE gene is also a major risk factor for AD and is associated with higher levels of Ab deposition in the brain. Correspondingly, the ApoE e2 allele is associated with a lower risk of AD-related neurodegeneration. The mechanisms modulating extended lifespan mediated by e2 compared to e3 and e4 genotypes are not clear. One hypothesis is that the ApoE e2 allele is neuroprotective and compensates for neuronal dysfunction induced by misfolded protein expression in aging and disease. In addition, the developmental program for the ApoE e2 allele may be distinct from the ApoE e4 allele. This is based on a body of literature that suggests the ApoE genotypes effect brain structure and gene expression beginning prenatal development and continuing into late life. Our proposed studies will utilize isogenic induced pluripotent stem cells (iPSCs) engineered with CRISPR/Cas9 to express the three isoforms of the ApoE protein (E2, E3 and E4). Using genetic engineering in preliminary studies, we generated lines carrying e2/e2, e3/e3 and e4/e4 genotypes in control iPSCs and Huntington?s Disease-HD-iPSCs. Recent advances in stem cell research suggest that iPSCs may provide novel models of aging and diseases. We will investigate using stem cell models the role of the exceptional longevity factor ApoE2 in aging and disease with the following Specific Aims: Specific Aim 1. We will characterize the cellular and functional differences in isogenic iPSCs with e2/e2, e3/e3 and e4/e4 genotypes using a systems biology approach. Specific Aim 2: To determine whether longevity-promoting ApoE variants enhance stress resistance and survival and identify the pathways relevant to the neuroprotective effects of the various variants. Specific Aim 3. We will determine if expression of ApoE2 or factors produced by ApoE cells provide increased health span in aged mice. Overall, our approach synergizes a number of unique methodologies to determine how naturally occurring genetic variants associated with Alzheimer?s disease modulate health span in multiple tissues and potentially lifespan. Successful completion of our proposed studies may reveal mechanisms with potential therapeutic exploitation for age-related disease and aging.